What is the normal thickness of the junctional zone and what does an abnormal thickness indicate?

Junctional Zone Thickness: Normal Values and Clinical Significance

I cannot provide actual images, but I can describe what normal and abnormal junctional zone thickness looks like on imaging and what these findings indicate clinically.

Normal Junctional Zone Thickness

The normal junctional zone thickness on MRI should not exceed 12 mm, though values up to 5 mm are most consistently normal across all uterine regions. 1, 2

• The junctional zone appears as a low signal intensity band on T2-weighted MRI between the endometrium and outer myometrium 3
• Mean normal thickness ranges from 4.3-4.4 mm in the anterior, posterior, and lateral walls of the uterine corpus 2
• The fundal region is typically thinner at 2.3 mm (range 1-5 mm) 2
• Important caveat: Up to 65% of normal women may have at least one region measuring >5 mm, and 30% may have two or more regions >5 mm, often due to transient myometrial contractions 2

Abnormal Junctional Zone Thickness

A junctional zone thickness ≥12 mm is the most established MRI criterion for diagnosing adenomyosis. 1, 4

What Abnormal Thickness Indicates:

• Adenomyosis: Thickening ≥12 mm strongly suggests ectopic endometrial glands and stroma infiltrating the myometrium 1, 5
• Endometriosis correlation: Women with pelvic endometriosis show significantly greater maximum JZ thickness (6.5 ± 1.9 mm) compared to those without endometriosis (4.8 ± 1.0 mm, P < .001) 6
• Impaired fertility: Increased JZ thickness is associated with poor implantation outcomes and may affect conception 4, 5
• Endo-myometrial unit disorder (EMUD): JZ thickening represents a distinct pathologic entity affecting the Müllerian-derived inner myometrium, separate from outer myometrial pathology 5

Imaging Characteristics on MRI

On T2-weighted images, the junctional zone normally appears as a smooth, uniform low-signal band. 3

• Disruption of this low-signal band indicates myometrial invasion by endometrial cancer 3
• Irregular thickening with high-signal foci on T2-weighted images suggests adenomyosis 1
• The junctional zone enhances on arterial phase dynamic contrast imaging, with an intact subendometrial enhancement line excluding myometrial invasion 3

Clinical Pitfalls to Avoid

• Do not use 5 mm as an absolute cutoff for adenomyosis diagnosis, as this results in high false-positive rates (up to 65% of normal women exceed this threshold) 2
• Transient myometrial contractions can cause focal thickening up to 12 mm in normal women, mimicking pathology 2
• JZ evaluation is difficult in postmenopausal women on T2-weighted images alone; use dynamic contrast enhancement to assess the subendometrial line 3
• Coexisting conditions like leiomyomas and endometrial polyps affect JZ contractility and may confound measurements 4

Alternative Imaging Modalities

Three-dimensional transvaginal ultrasound (3D-TVUS) provides excellent visualization of the junctional zone with 92% accuracy for Müllerian anomalies. 7, 6

• 3D-TVUS allows multiplanar assessment of JZ thickness and alterations 6
• MRI remains the gold standard with 100% accuracy for complex uterine pathology 7
• Standard 2D ultrasound can visualize the JZ as a subendometrial halo but is less reliable for precise measurements 5